1. Field of the Invention
The present invention relates to a pressure container manufacturing method and particularly, to a pressure container manufacturing method for manufacturing a pressure container which is reinforced by covering a liner with a fiber reinforced composite material.
2. Description of the Related Art
Currently, a pressure container for storing and transporting compressed gas such as CNG (Compressed Natural Gas), CHG (Compressed Hydrogen Gas) or the like, or low temperature gas has been in practical use. Earlier, a pressure container made of metal which has high strength and is excellent in gas barrier property has been mainstream, however due to its heavy weight, there is a difficulty in applying it to a fuel tank of an automobile or a space plane in which weight saving is required. Therefore, recently, there has been proposed a relatively light weight FRP (Fiber Reinforced Plastics) wrapped pressure container which is made by forming an FRP layer on the periphery of a hollow cylindrical liner.
There are a FW (Filament Winding) method and a TW (ape Winding) method as a method to form the FRP layer on the periphery of the hollow cylindrical liner. The FW method is a method in which fiber bundles are impregnated with resin beforehand to prepare a tow shaped prepreg and an FRP layer is formed by winding the tow shaped prepreg on the liner, or a method in which fiber bundles which are fed in a predetermined direction are impregnated with resin to be wound around a liner. The TW method is a method in which a tape shaped prepreg is wound around the liner to form an FRP layer. Applying the FW method or the TW method is successful in obtaining an FRP wrapped pressure container which is relatively light in weight and has high strength.
However, applying the FW method or the TW method would raise a problem of requiring a long period of time to wind the tow shaped or tape shaped continuous prepreg on the liner. For example, it will take about 8 hours to manufacture a CNG tank (400 mm in diameter, and 1000 mm in length) for 200 atmospheres of CNG which is installed in a vehicle.
To solve this problem, recently, there has been proposed a “braiding method” in which a braider is used to form a body on the periphery of the liner by braiding a plurality of fiber bundles, and the body is impregnated with resin to be cured to form the FRB layer (for example, refer to JP-Tokukaihei-11-58540A (Page 3, FIG. 4) or JP-Tokukaihei-7-256771A (Page 2, FIG. 2)). Applying the braiding method is successful in shortening the manufacturing time and reducing the manufacturing cost of the pressure container compared with the case of applying the FW method or the TW method.
In the earlier developed “braiding method”, fiber bundles which are not impregnated with resin such as a dry CF (Carbon Fiber) or the like are often used to reduce the resistance while braiding. However, since the bundle which is not impregnated with resin does not have adhesiveness like the prepreg, the fiber bundles may loosen while braiding. Such looseness of the fiber bundles would be a main cause of reducing the strength of the FRP layer. Also, in the earlier developed “braiding method”, a plurality of fiber bundles is crossed, so that the fiber bundles are bent at crossing portions, thereby loosening the bundles. Increasing the amount of the fiber bundles for keeping the strength of the FRP layer would raise problems of increasing the weight of the pressure container and raising the manufacturing cost.